The present invention generally relates to rotation stopping apparatuses for motors, and more particularly to an apparatus stopping rotation of a motor with high accuracy and maintaining the motor in a stopped state by use of a simple rotation stoppage detection circuit.
Generally, a motor (Hall motor) using a Hall element is capable of rotating towards forward and reverse directions. In order to stop a rotor rotating in the forward direction, a torque (reverse torque) in the reverse direction is applied to the rotor. However, when the reverse torque is applied to the rotor to stop the rotation of the rotor, although the rotational speed of the rotor is reduced instantaneously reduced to zero, the rotor will start to rotate in the reverse direction thereafter if the reverse torque is continued to be applied to the rotor. Accordingly, in order to perfectly stop the rotation of the rotor, it is necessary to detect the stoppage of rotation of the rotor and stop the reverse torque from being applied to the rotor.
Hence, various detection circuits for detecting the stoppage of rotation of the rotor, have conventionally been proposed. As an example of a conventional rotation stoppage detection circuit, there was a circuit in which it is detected that the rotational speed of the rotor has become substantially one-tenth of the rotational speed upon constant rotation by use of a voltage comparator, to pass the detected output through a delay circuit, and use the delayed output as a rotation stoppage detection signal to stop the application of the reverse torque with respect to the rotor. In this case, the time it takes for the rotational speed of the above rotor to reach zero from the rotational speed which is substantially one-tenth that upon constant rotation is measured and estimated in advance, and the delay time of the above delay circuit is set to the above estimated time.
However, in the above conventional circuit, the stoppage of rotation of the rotor is not directly detected, and the rotation stoppage signal is produced at the point in time which has been preset by the delay circuit. Hence, there was a disadvantage in that the operation to stop the rotation of the rotor could not be performed with high accuracy. Moreover, there was a disadvantage in that the circuit construction became complex, since the circuit used a voltage comparator, a delay circuit, and the like.
On the other hand, as another conventional circuit, there was a circuit in which the rotational speed of the rotor is counted by a digital counter, and it is detected that the rotational speed of the rotor has become equal to or below a predetermined value, to cut off the power source with respect to a motor driving circuit. However, the circuit construction of this conventional circuit is complex since digital circuits such as a digital counter are used, and there was a disadvantage in that the circuit could not be constructed at low cost.
Furthermore, in the conventional motor driving circuit, even when the application of the reverse torque with respect to the rotor is stopped, in a case where the rotor receives an external force urging rotation in the reverse direction due to some cause, a torque in the reverse direction is applied to the motor. In this case, the motor unnecessarily starts to rotate in the reverse direction.